文献翻译——一种新的数字化设计与分析图像加密方案

第1页外文文献资料InternationalJournalofNetworkSecurity&ItsApplications(IJNSA),Vol.4,No.2,March2012DOI:10.5121/ijnsa.2012.420795DESIGNANDANALYSISOFANOVELDIGITALIMAGEENCRYPTIONSCHEMENarendraKPareekUniversityComputerCentre,VigyanBhawan,MLSukhadiaUniversity,Udaipur-313001,IABSTRACTInthispaper,anewimageencryptionschemeusingasecretkeyof144-bitsisproposed.Inthesubstitutionprocessofthescheme,imageisdividedintoblocksandsubsequentlyintocolorcomponents.Eachcolorcomponentismodifiedbyperformingbitwiseoperationwhichdependsonsecretkeyaswellasafewmostsignificantbitsofitspreviousandnextcolorcomponent.Threeroundsaretakentocompletesubstitutionprocess.Tomakeciphermorerobust,afeedbackmechanismisalsoappliedbymodifyingusedsecretkeyafterencryptingeachblock.Further,resultantimageispartitionedintoseveralkeybaseddynamicsub-images.Eachsub-imagepassesthroughthescramblingprocesswherepixelsofsub-imagearereshuffledwithinitselfbyusingageneratedmagicsquarematrix.Fiveroundsaretakenforscramblingprocess.Theproposeschemeissimple,fastandsensitivetothesecretkey.Duetohighorderofsubstitutionandpermutation,commonattackslikelinearanddifferentialcryptanalysisareinfeasible.The第2页experimentalresultsshowthattheproposedencryptiontechniqueisefficientandhashighsecurityfeatures.KEYWORDSEncryption,Secretkey,Substitution,Scrambling,Security,Imagecipher.1.INTRODUCTIONWiththerapidgrowthofcomputernetworksandadvancesininformationtechnology,ahugeamountofdigitaldataisbeingexchangedoverunsecuredchannels.Majorpartoftransmittedinformation,eitherconfidentialorprivate,demandsforsecuritymechanismstoproviderequiredprotection.Therefore,securityhasbecomeanimportantissueduringthestoringandtransmissionofdigitaldata.Thesecurityofimagesisanapplicationlayertechnologytoguardthetransmittedinformationagainstunwanteddisclosureaswellastoprotectthedatafrommodificationwhileintransit.Itincludesseveralaspectslikecopyrightprotection,authentication,confidentialityandaccesscontrol.Itisarguedthattraditionalencryptionalgorithmsarenotpreferableforimageencryptionfortworeasons.Oneisthattheimagesizeisalwaysmorethantextsize.Therefore,traditionalcryptosystemstakelongertimetoencrypttheimagedata.Theotheristhatthesizeofdecryptedtextmustbeequaltotheoriginaltextsize.However,thisrequirementisnotnecessaryforimagedata.Duetothecharacteristicofhumanperception,asmalldistortionindecryptedimageisusuallyacceptable.Threedifferentwaystoprotectdigitaldatafromunauthorizedeavesdroppingarecryptography,steganographyandwatermarking.Amongthesethreetechniques,cryptographyhasbecomeoneofthemajortoolstoprovidehighlevelofsecurity.Cryptographydealswiththedevelopmentoftechniquesforconvertinginformationbetweenintelligibleandunintelligibleforms.Itdealswiththecontentconfidentialityandaccesscontrol.Insecurecommunicationsusingcryptography,whichisthemainfocusofthepresentwork,theencryptionanddecryptionoperationsareguidedbyoneormorekeys.Techniquesthatuse第3页samesecretkeyforencryptionanddecryptionaregroupedunderprivatekeycryptography.Alternately,encryptionanddecryptionkeysaredifferentorcomputationallyitmaynotbefeasibletoderiveonekeyeventhoughtheknowledgeofotherkey,suchcryptographicmethodsareknownaspublickeycryptography.Thepresentworkfocusesonthedevelopmentofprivatekeyimagecryptographicalgorithmforprovidinghighlevelofsecurity1.1RelatedworkInordertoprotectdigitalimagesfromunauthorizedusersdoingillegalreproductionandmodifications,avarietyofimageencryptionschemeshavebeenproposed.Thevariousideasusedintheexistingimageencryptiontechniquescanbeclassifiedintothreemajorcategories:positionpermutation1,2,7,10,valuetransformation3,4,8,12andthecombinationform5,6,9,11,13,14.Thepositionpermutationalgorithmsscramblethedatapositionwithintheimageitselfandusuallyhavelowsecurity.Ontheotherhand,thevaluetransformationalgorithmstransformthedatavalueoftheoriginalsignalandhavethepotentialoflowcomputationalcomplexityandlowhardwarecost.Finally,thecombinationformsperformbothpositionpermutationandvaluetransformationandusuallyhavethepotentialofhighsecurity.Inrecentyears,anumberofdifferentimageencryptionschemeshavebeenproposedinordertoovercomeimageencryptionproblems.Afewimageencryptiontechniquessuggestedrecentlyarediscussedinthefollowingparagraphinbrief.In2010,YoonandKim7developedachaoticimagecipherinwhichinitiallyasmallmatrixwasgeneratedusingchaoticlogisticmap.Authorsconstructedalargepermutationmatrixfromgeneratedsmallmatrixes.Theconstructedpermutationmatrixwasusedtopermuteplainimagepixels.Further,anewchaoticimagecipherwassuggestedbyIsmailetal8inwhichtheyusedtwochaoticlogisticmapsaswellasanexternalsecretkeyof104-bitssize.Controlparametersforbothchaoticlogisticmapsweregeneratedfromtheusedexternalsecretkey.Theyalsoemployedafeedbackmechanismintheirimageciphertomakesystemmoresecured.In2011,JolfaeiandMirghadri9suggestedachaotic第4页imagecipherbasedonpixelshuffling,usingbakermap,andmodifiedversionofsimplifiedAES(S-AES),developedbyMusaetal.in200315.Further,Nayaketal.10proposedachaoticimagecipherusinglogisticmap.Inthealgorithm,permutationofimagepixelswasmadeonthebasisofindexpositionofgeneratedchaoticsequence.SathishkumarandBagan11suggestedachaoticimagecipherbasedinwhichblockpermutation,pixelpermutationandvaluetransformationwereused.Next,chaoticimagecipherusingtwochaoticlogisticmapsandasecretkeyof80-bitswassuggestedbyChenandChang12.IndrakantiandAvadhani13developedanon-chaoticimagecipherinwhichencryptionwasachievedinthreeprocesses.Inthelastprocess,akeywasgeneratedwhichkeepallinformationaboutencryptionprocess.Next,Xinetal20proposedachaosbasedcryptosystembasedondiffusionandconfusion.Toimprovethesecurityoftheconfusionmodule,authorsintroduceddiffusionmechanisminconfusionstagethroughalightweightbitlevelpermutationalgorithm.Pengetal21proposedanimageblockencryptionalgorithmbasedonthreedimensionalChenchaoticdynamicalsystem.Thealgorithmusedasecretkeyof192-bitsizewithanimageblockof32-bitlong.Inthealgorithm,ChenssystemgeneratedachaoticsequencethatwasinputtedtoadesignedfunctionGwhichwasiteratedseveraltimes.Further,Sathishkumaretal22suggestedanimageencryptionschemeusingmultiplechaoticbasedcircularmapping.Basedontheinitialconditions,eachmapproducesrandomnumbersfromorbitsofthemaps.Amongthoserandomnumbers,aparticularnumberfromaparticularorbitwasselectedasakeyfortheencryptionalgorithm.Further,inputimagewasreshuffledanddividedintovarioussub-blocks.Thenthepositionpermutationandvaluepermutationwasappliedtoeachbinarymatrixbasedonmultiplechaosmaps.Jameietal23proposedanimageencryptionusingchaoticsignalsandcompletebinarytree.Inthemethod,perfectbinarytreewasutilizedtoincreasecomplexityintheencryptionalgorithm.Next,Sathyanarayanaetal24designedanencryptionalgorithmfocusingontheapplicationofpropertiesoffinitefieldsandellipticcurves.AdditiveandAffineencryptionschemesusingsixschemesofkeysequencesobtainedfromrandomellipticcurvepointsweredesigned.Inthedevelopedalgorithm,cyclicellipticcurvesoftheformy2+xy=x+ax2+b,a,b第5页GF(2m),b_0withorderMwasconsideredinthedesignofasymmetrickeyimageencryptionscheme.Pareeketal25proposedalosslessdigitalimageencryptionschemebasedonthepermutationandsubstitutionarchitecture.Inthealgorithm,plainimagewasdividedintosquaredsub-imagesandthenreshuffledthem.Further,inthepermutationprocessasimplearithmetic,mainlysortinganddifferencing,wasperformedtoachievethesubstitution.HybridmodelofcellularautomataandchaoticsignalwasproposedforimageencryptionbyFateriandEnayatifar26.Inthismethod,8-bitsmaskwasusedforchangingthepixelgraylevelofmainimage.Forchangingeachpixelgraylevel,valueofeachbitofthemaskwasselectedbyoneofthe256cellularautomatstandardrules.Oneofthe256cellularautomatstandardruleswasdeterminedbychaoticsignal.1.2PaperoutlineInavailableliterature,mostofsuggestedimageencryptionschemesarebasedonchaoticdynamicalsystem.Inthispaper,anon-chaosbasedimageencryptionschemeusinganexternalkeyof144-bitsispresented.Theproposedencryptionschemeusesbothpixelsubstitutionaswellaspixelpermutationprocess.Afeedbackmechanism,toavoiddifferentialattackandmakethecryptosystemmorerobust,isalsoapplied.Theproposedencryptionschemehashighencryptionrate,requireslesscomputationandsensitivetosmallchangesinthesecretkeysoevenwiththeknowledgeoftheapproximatekeyvalues,thereisnopossibilityfortheattackertobreakthecipher.Theproposedschemeissimple,fastandsecuredagainstanyattack.Therestofthepaperisorganizedinthefollowingmanner.Insection2,variousprocessesusedintheproposedalgorithmaswellasdetailofencryptionalgorithmisdiscussed.SimulationresultsandsecurityanalysisareprovidedinSection3.Finally,theconclusionsaredrawninSection4.2.PROPOSEDENCRYPTIONALGORITHMImagedatahavestrongcorrelationsamongadjacentpixelsformingintelligibleinformation.Toencrypttheimage,thisintelligibleinformationneedstobereducedbydecreasingthecorrelationamongtheadjacentpixels.Theproposedencryptionalgorithmdoesthisbymodifyingthepixelvaluesoftheimageaswell第6页asreshufflingthepixelsoftheresultantimagewithinitself.Infollowingparagraph,functionsofvariousprocessesusedintheproposedalgorithmarediscussed.2.1KeymixingprocessTwokindsofkeymixingprocesses,calledFKMandBKM,areusedintheproposedalgorithm.Inboththeprocesses,imageblockisdividedintosub-blocks(p1,p2.p18)andeachsub-block(pi)ismodifiedbyusingsub-key(ki),itsprevioussub-block(pi-1)andsub-block(pi)itself.AsimilarprocessisusedintheBKMprocess.Forwardkeymixing(FKM)processi=2temp=p1,p1=p1k1if(i=1)thentemp1=pi,pi=pikitemp,temp=temp1elsei=i-1endif2.2Substitutionprocess第7页Inthisprocess,bitwiseoperationsareperformedonpixelsofsub-blockstochangetheirproperties.PictorialviewofsubstitutionprocessusedintheproposedsystemisshownintheFigure(1)anditsequivalentdescriptionisasfollows:1.Takeaplainimageblockanddivideditintoeighteenequalsub-blocksnamedasp1,p2,p3.p18.2.setposition=53.seti=1,Ti=pi4.if(position=5)thenpi=pi(kjmod18)5.bv=Tiposition6.seti=i+1,Ti=pi7.performoperationonpiasshowninTable(1)8.if(iN)or(SubImagerowcol#0)thenrow=row+2,col=col-1elseif(row=0)thenrow=Nelseif(colN)thencol=1endInthefollowingexample,howpositionsofpixelsarereshuffledwithinsub-imageisshown.Pixelsofsub-imageofdimension5x5areshowninTable2(a).Further,amagicsquareofsamedimensionisconstructedasshowninTable2(b).Now,permutepixelofsub-imagereferencingconstructedmagicsquare.Theresultantsub-imagepixelsareshownintheTable2(c).TABLE2.PIXELOFASUB-IMAGE,MAGICSQUAREMATRIXANDPIXELOFRESULTANTSUB-IMAGEISSHOWNIN(A),(B)AND(C)RESPECTIVELY.2.4TheCompleteencryptionalgorithmProposedalgorithmhastwomajorprocesses-pixelssubstitutionandpixelspermutation.Bothsubstitutionandpermutationprocessesarecompletelysecretkeydependent.Afeedbackmechanismisappliedinsubstitutionprocesstoavoiddifferentialattack.Stepsofalgorithmarediscussedbelow.第12页1)Theproposedencryptionschemeusesasecretkeyof144-bitssize.Thesecretkeyisdividedintoeighteenequalpartsof8-bitseachreferredassub-keys.k=k1k2k3k18.(1)2)Plainimageisdividedintoseveralblockscomprisingeighteenbyteseach.3)Eachimageblockispassedthroughthesubstitutionprocess.Whenaprocessingofablockisover,thekeyismodifiedfromitspreviouslyencryptedimageblock.Resultantpixelsarewritteninafile.4)setiteration=55)Takeoriginalsecretkeyandgeneratekeydependentoddintegerrandomnumberintherange50to200,sayN,usinganyrandomnumbergenerator.6)Partialencryptedimageisdividedintoseveralnon-overlappingsquaredsub-imageseachofsizeNxN.7)Takesub-imagesonebyoneandpassesthroughthepermutationprocess.8)Decreaseroundsvaluebyoneandrepeattheabovestepsfrom(5)tilliterationvalueisnon-zero.Finally,theencryptedpixelsofthesub-imagearewritteninafile.3.PERFORMANCEANDSECURITYANALYSISSeveraltestsonUSC-SIPIimagedatabase(freelyavailableat/database/)tojustifythesecurityandperformanceoftheproposedimagecipherhavebeendone.Anidealimageciphershouldresistagainstallkindsofknownattackssuchascryptanalytic,statisticalandbruteforceattacks.Inthissection,securityanalysisoftheproposedimageencryptionschemesuchasstatisticalanalysis,keyspaceanalysis,sensitivityanalysisetctoprovethattheproposedimagecipheriseffectiveandsecureagainstthemostcommonattacksisdiscussed.TheproposedalgorithmhasbeenimplementedinCprogramminglanguage.Fortheanalysisofimagedata,Matlabapplicationtoolwasused.3.1Statisticalanalysis第13页Intheliterature,itwasfoundthatmostoftheexistingimageciphershavebeensuccessfullycryptanalyzedwiththehelpofstatisticalanalysis.Toprovetherobustnessoftheproposedencryptionscheme,statisticalanalysishasbeenperformedwhichdemonstratesitssuperiorconfusionanddiffusionpropertiesresultsinastronglyresistingnatureagainstthestatisticalattacks.Thisisdonebytestingthedistributionofpixelsofthecipherimages,studyofcorrelationamongtheadjacentpixelsinthecipherimage,informationentropyandthecorrelationbetweentheplainandcipherimages.3.1.1DistributionofpixelsHistogramsofseveralcipherimagesandtheircorrespondingplainimageshavingwidelydifferentcontentsandsizeshavebeenanalysed.OneexampleofhistogramanalysisforwellknownimageLenaisshowninFigure2.Histogramsofred,blueandgreencomponentsofimage(Figure2(a)areshowninFrames(b),(c)and(d)respectively.InFrames(f),(g)and(h)respectively,thehistogramsofred,blueandgreencomponentsofthecipherimage(Figure2(e)areshown.Comparingthehistograms,itisfoundthatencryptionprocessreturnsnoisyimages.Histogramsofcipherimages,approximatedbyuniformdistribution,arequitedifferentfromthatoftheplainimageandcontainnostatisticalresemblancetotheplainimage.ThisisconsistentwiththeperfectsecuritydefinedbyShannon16andtheproposedencryptionschemeresistsagainsttheknown-plaintextattack.第14页FIGURE2.HISTOGRAMSCORRESPONDINGTORGBCOMPONENTSOFPLAINIMAGELENAANDITSCORRESPONDINGCIPHERIMAGE.3.1.2CorrelationbetweenplainandcipherimagesAnextensivestudyofthecorrelationbetweenpairsofplainimageandtheircorrespondingcipherimageproducedusingtheproposedencryptionschemebycomputingcorrelationcoefficient(CR)betweenRGBcomponentsoftheplainimagesandcorrespondingcipherimageshavebeendone.ResultsforafewimagesareshowninTable3.SincethecorrelationcoefficientsshownintheTable3areverysmall(C0),itindicatesthattheplainimagesandtheircorrespondingcipherimagesarecompletelyindependentofeachother.第15页TABLE3.CRBETWEENPLAINIMAGESANDTHEIRCORRESPONDINGCIPHERIMAGES3.1.3CorrelationanalysisofadjacentpixelsCorrelationsbetweentwoverticallyandhorizontallyadjacentpixelsinvariousplainimagesandtheircorrespondingcipherimageshavebeenanalysed.InFigure3,thedistributionsofhorizontallyadjacentpixelsofred,greenandbluecomponentsintheimageLenaandtheircorrespondingcipherimageisshown.Particularly,inFrames(a),(b)and(c),depictthedistributionsoftwohorizontallyadjacentpixelsofred,greenandbluecomponentsrespectivelyintheplainimage(Figure2(a).SimilarlyinFrames(d),(e)and(f)respectively,thedistributionsoftwohorizontallyadjacentpixelsinitscorrespondingcipherimage(Figure2(e)havebeendepicted.Similarly,inFigure4,thedistributionsofverticallyadjacentpixelsofred,greenandbluecomponentsintheplainimageLenaanditscorrespondingcipherimageisshown.ItisobservedfromcorrelationchartsandTable4thatthereisanegligiblecorrelationbetweenthetwoadjacentpixelsinthecipherimage.However,thetwoadjacentpixelsintheplainimagearestronglycorrelated.Correlationinthecipherimagesisverysmallornegligiblewhentheproposedencryptionschemeisused.Hencetheproposedschemehasgoodpermutationandsubstitutionproperties.第16页TABLE4.CRFORTWOADJACENTPIXELSINTHEPLAINANDITSCIPHERIMAGE.3.1.4InformationentropyIllegibilityandindeterminatenessarethemaingoalsofimageencryption.Thisindeterminatenesscanbereflectedbyoneofthemostcommonlyusedtheoreticalmeasure-InternationalJournalofNetworkSecurity&ItsApplications(IJNSA),Vol.4,No.2,March2012103informationentropy.Informationentropyexpressesthedegreeofuncertaintiesinthesystemanddefinesasfollow.whereP(mi)istheemergenceprobabilityofmi.Ifeverysymbolhasanequalprobability,i.e.,m=m0,m1,m2,m28-1andP(mi)=1/28(i=0,1,255),thentheentropyisH(m)=8whichcorrespondstoanidealcase.Practically,theinformationentropiesofencryptedimagesarelesscomparedtotheidealcase.Todesignagoodimageencryptionscheme,theentropyofencryptedimageclosetotheidealcaseisexpected.InformationentropyforafewimagesisshowninTable5whichisH(m)=7.73andveryclosetotheidealvalue.Thismeansahighpermutationandsubstitutionisachievedbytheproposedalgorithmandhasarobustperformanceagainsttheentropyattack.第17页TABLE5.ENTROPYFORDIFFERENTIMAGES3.2KeysensitivityanalysisAnidealimageciphershouldbeextremelysensitivewithrespecttothesecretkeyusedinthealgorithm.Flippingofasinglebitinthesecretkey,itshouldproduceawidelydifferentcipherimage.Thisguaranteesthesecurityofacryptosystemagainstbrute-forceattackstosomeextent.Sensitivitywithrespecttoatinychangeinthesecretkeyforseveralimageshavebeentested.OneexampleforplainimageLenaisdiscussedbelow:a.Plainimage(Figure2(a)isencryptedbyusingthesecretkeyC6DA750B4C1F78D329EA25E6B15CF9E47D21andtheresultantencryptedimageisreferredasimageFigure5(a).b.Theencryptedimage(Figure5(a)isdecryptedbymakingaslightmodificationintheoriginalkeyB6DA750B4C1F78D329EA25E6B15CF9E47D21andtheresultantdecryptedimageisreferredasimageFigure5(b).c.Theencryptedimage(Figure5(a)isdecryptedbymakingaslightmodificationintheoriginalkeyC6DA750B4C1F78D329EA25E6B15CF9E47D22andtheresultantdecryptedimageisreferredasimageFigure5(c).d.Theencryptedimage(Figure5(a)isdecryptedbymakingaslightmodificationintheoriginalkeyC6DA750B4C1F78D329FA25E6B15CF9E47D21andtheresultantdecryptedimageisreferredasimageFigure5(d).第18页Withasmallchangeinthekeyatanyposition,oneisnotabletorecovertheoriginalimage.Itisnoteasytocomparedecryptedimagesthroughthevisualinspection.Tocomparedecryptedimages,correlationcoefficientbetweenencryptedimagesandvariousdecryptedimageswascalculatedandresultsaregiveninTable6.Thecorrelationcoefficientsarenegligible.Havingtherightpairofsecretkeyisanimportantpartwhiledecryptingtheimage,asasimilarsecretkey(withonebitchange)willnotretrievetheexactoriginalimage.Aboveexampleshowstheeffectivenessoftheproposedtechniqueasthedecryptionwithaslightlydifferentsecretkeydoesnotrevealanyinformationtoanunauthorizedperson.FIGURE3:DISTRIBUTIONSOFHORIZONTALLYADJACENTPIXELSOFRGBCOMPONENTSINTHEPLAINIMAGELENAANDITSCIPHERIMAGE.第1